[FPSPACE] FW: NEO News (04-17-06) Dawn, Planetary Defense, Comets
ljk4 at msn.com
Tue Apr 18 16:35:33 EDT 2006
>From: David Morrison <dmorrison at arc.nasa.gov>
>To: David Morrison <dmorrison at arc.nasa.gov>
>Subject: NEO News (04-17-06) Dawn, Planetary Defense, Comets
>Date: Mon, 17 Apr 2006 17:29:19 -0700
>NEO News (04-17-06) Dawn, Planetary Defense, Comets
>Following are three stories, one announcing the next Planetary Defense
>Conference (March 2007) and the other two stories dealing with new ideas on
>the nature of comets. First, however, the good news of the reinstatement of
>the Dawn Discovery mission, which will orbit the largest main-belt
>asteroids, Ceres and Vesta. On 1 March we reported that NASA had decided on
>the "indefinite postponement" of this mission, and a few days later NASA
>announced its cancellation. However, a formal cancellation review
>subsequently gave the mission a clean bill of health, concluding that major
>technical difficulties seemed to have been overcome, and therefore NASA has
>decided to continue with the mission.
>2007 PLANETARY DEFENSE CONFERENCE: CALL FOR PAPERS
>5-8 March 2007
>George Washington University
>Papers are now being solicited for the 2007 Planetary Defense Conference.
>To download a copy of the Call for Papers, go to
><http://www.aero.org/conferences/planetarydefense/cfp.pdf>. This conference
>will consider planetary protection from the systems prospective and cover
>the following areas:
>* Detect and define the threats
>* Look at deflection options and available technologies
>* Examine recent missions with an eye towards lessons learned for
>* Discuss characteristics of candidate missions to mitigate the threats
>* Consider the policy and disaster preparedness implications.
>Participants will develop a set of recommended actions to improve our
>ability to successfully defend Earth from possible impacts.
>This is the second Planetary Defense Conference and will be repeated every
>several years to assess progress, incorporate new technology and provide an
>ongoing focus to this important work.
>Depending on funds available, a limited number of honoraria will be awarded
>to invited speakers. To encourage student participation, a limited number
>of scholarships will be awarded to students whose papers are judged by the
>steering committee as being particularly relevant to the conference goals
>and focus areas.
>A goal of the conference is to focus on technologies, capabilities, and
>issues that in the next 15 years are likely to affect the decision to
>undertake a deflection mission, to enable a deflection, to prepare the
>public for a deflection effort, or to respond to an impact-related
>disaster. Authors should keep this in mind as they prepare their abstracts
>Technical paper abstracts (no less than 500 words in length and in pdf
>format) will be accepted electronically at <asteroid at aero.org> beginning 2
>March 2006. Please be sure to designate to which topic area your paper
>correlates. Papers dealing with education and design in the identified
>categories, as well as international collaboration projects, are invited
>and encouraged. Abstracts may include key figures and references to
>pertinent publications in existing literature.
>Accepted papers will be published on the conference Web site and will be
>included on the conference CD-ROM. Most speakers at the conference will be
>invited, but a limited number of submitted papers may be selected for
>presentation. The remainder of accepted papers will be posters. Authors of
>all poster papers will be able to present a two-minute, two-slide
>presentation during the regular session. With their final manuscripts,
>authors must include a cover letter that indicates they have received the
>appropriate company and/or sponsoring agency approval for public release.
>The format for papers will be provided on the conference Web site at a
>The deadline for receipt of abstracts via electronic submission is 13
>October 2006. Technical program chairs will notify authors of conditional
>acceptance or rejection on or before 3 November 2006. Letters of official
>acceptance and instructions will be mailed on or before 10 November 2006.
>The deadline for submission of the final written paper is 16 February 2007.
>The 2007 Planetary Defense Conference is sponsored by:
>The American Institute of Aeronautics and Astronautics (AIAA)
>The Aerospace Corporation
>Space Studies Institute (SSI)
>SpaceWorks Engineering, Inc.
>CLANDESTINE COMETS FOUND IN MAIN ASTEROID BELT
>23 March 2006
>NewScientist.com news service
>You do not have to look to the outer edges of the solar system, or even out
>beyond Neptune to observe a reservoir of comets. A bevy of the
>ice-containing bodies lies disguised as main-belt asteroids between Mars
>and Jupiter, claim astronomers from the University of Hawaii, US.
>David Jewitt and Henry Hsieh have dubbed the new population "main belt
>comets". They describe three objects with near circular, flat orbits in the
>asteroid belt that stream volatile materials, producing an observable tail
>for weeks and months at a time.
>The finding backs a theory that ice-bearing asteroids - or "comets" - from
>this much closer region may have played an important role in forming the
>Scientists once believed the icy comets from the outer regions of the solar
>system were the most likely source of the water that transformed the early
>Earth from a dry, barren world. But chemical analyses of comet water -
>carried out from a distance - ruled out the possibility.
>Another possibility was asteroids. But it had seemed impossible to study
>the water content of asteroids since most of their water appears to have
>dissipated or is now buried too deeply to observe.
>Now Jewitt says this new population within the asteroid belt may provide a
>way to sample the chemicals in water on or near the surface of these
>objects. And he says the main-belt comets hold promise for future study as
>components of the protoplanetary disc that surrounded the Sun - the disc
>from which the planets formed. "They're a window to some early epoch, back
>when objects were accreting," he says.
>The new study underscores the increasingly hazy distinction between comets
>and asteroids. "There are different definitions of comet used by different
>people at different times," Jewitt told New Scientist.
>The two traditionally recognised comet reservoirs are the Kuiper Belt, a
>frigid region beyond Neptune's orbit, and the even more distant Oort Cloud.
>One definition describes a comet as an object following a highly
>elliptical, often inclined orbit with origins in one of these two
>But another definition involves what an observer sees either with the naked
>eye or through a telescope - a comet's streaming gassy tail as it loses ice
>and other volatile materials through being warmed by the Sun.
>Jewitt says based on their nearly circular, stable orbits, the main belt
>comets are "completely asteroidal". You would never guess that they were
>anything but asteroids." But in terms of appearance, with their
>long-lasting tails, he says "they're definitely comets".
>The team believes in order to survive at such proximity to the Sun, the
>volatiles in the main belt comets would have to be covered by a layer of
>possibly carbonaceous material. They say an impact event could then uncover
>some of the volatiles, allowing the Sun's heat to trigger the observed
>Asteroid expert Richard Binzel at MIT questions the need for the new
>classification. "I prefer to think of them as activated asteroids," he told
>New Scientist. "It's no surprise if some asteroids have some water content,
>particularly in the outer asteroid belt."
>He says volatiles have been measured to make up about 10% of some
>carbonaceous meteorites that are thought to come from the region.
>Jewitt says potentially tens of thousands of main belt objects contain ice
>and have simply not been observed during their active period. In order to
>be seen spewing dust, the objects would have to have been hit by a meteor
>size boulder within the last thousand years or so, he adds.
>Journal reference: Science (DOI: 10.1126/science.1125150)
>THE COMETS' TALE: MAYBE THE DIRTY SNOWBALL THEORY IS WRONG
>by David L. Chandler
>The Boston Globe
>April 10, 2006
>Three fly-by missions since 2001 have confounded almost everything
>astronomers thought they knew about the makeup of comets. Then, two weeks
>ago, University of Hawaii researchers announced the discovery of a whole
>new family of close-in comets -- which might help explain how the early
>Earth got its water.
>Our lack of knowledge could have dire consequences, scientists warn,
>because -- unlike asteroids, whose paths can be predicted years in advance
>-- comets could strike Earth with little warning. The missions have proven
>that we don't know enough about these dazzling lumps of ice and dirt to
>know how to respond.
>But now, one astronomer has come up with a theory that might tie some of
>the loose ends together. Instead of the conventional view of a comet's
>nucleus as a solid, several-miles-wide rubble pile or dirty snowball,
>Michael Belton, a lead scientist for last year's Deep Impact comet mission,
>suggests that the nucleus may be more like a lump of papier mache -- built
>up from a random assortment of irregular sheets of varying thickness.
>''The presence of layers is ubiquitous" in the nuclei seen so far, Belton
>said, ''and may be an essential element of their internal structure." In
>his view, the nuclei were built up gradually as hundreds of smaller bodies
>smashed together over time, each flattening out and sticking to the growing
>body, forming one layer after another.
>Astronomers were startled and confused by the dramatic and unexpected
>differences between the nuclei of Tempel 1 (seen by last year's Deep Impact
>mission), Wild 2 (as seen by the Stardust mission in 2004) and Borrelly
>(seen by deep Space 1 in 2001).
>Belton's new theory, which he outlined at a conference in Houston last
>month, identifies all the varied and unexplained features seen on these
>comets -- including supposed craters on Wild 2, mesa-like plateaus on
>Borrelly, and distinctly different, overlapping surface textures on Tempel
>1 -- as different aspects of the layered model he nicknamed Talps (for
>''splat" spelled backwards).
>Clark Chapman, a specialist in asteroids and comets at the Southwest
>Research Institute in Boulder, Colo., agrees with Belton that ''it looks
>like comets have layers in them," but he said the theory is still untested.
>''It's a first step toward trying to understand comets differently."
>The new model would have significant implications for the life cycle of
>comets and for how we might attack a comet headed for Earth. Pushing aside
>a solid ball with a huge rocket or nuclear blast might make sense, but
>using the same approach against a ball of many layers might cause the comet
>to splinter and could magnify the damage rather than avert it, Belton
>The find of a new type of comet -- the third known -- adds a lot of new
>questions to comet research and possibly helps answer a longstanding
>mystery: How the Earth has so much water when models suggest it shouldn't.
>As the solar system's inner planets coalesced from the cloud of gas and
>dust swirling around the sun, the sun's heat caused water to evaporate. The
>new discovery suggests that Earth's water supply might have been
>replenished by some comets or asteroids that initially formed just a bit
>farther out and so might have retained their ice as they hurtled around the
>sun and eventually smashed into our planet.
>Astronomers Henry Hsieh and David Jewitt of the University of Hawaii
>announced late last month that they have found comets with asteroid-like
>orbits -- circling the sun as planets do, between Mars and Jupiter, instead
>of the very elongated orbits characteristic of all previously known comets.
>Finding comets like these suggests that there could be icy asteroids or
>comets that formed much closer to the sun than previously thought. They
>would have replenished Earth's water supply when they crashed into its
>''I think it's very significant," Jewitt said, to find such a fundamentally
>different group of comets, which must have formed separately from all the
>others. But it will take more study to figure out how this new population
>will compare to the others and what kind of structure they might have.
>Being born in a hotter region of the growing solar system, for example,
>might have produced a different kind of layering, if any.
>Belton, president of Belton Space Exploration Initiatives in Tucson, said
>he'd like to have a chance to prove his model by getting a closer look at
>some of these comets, particularly with a radar analysis -- which past
>missions couldn't perform -- that could clearly show whether the orb is
>layered deep down.
>It may be a while before he gets that wish, but the European Space Agency's
>Rosetta mission will provide close-up views in 2014 of another comet
>nucleus and will use microwaves to probe its inner structure. Other comet
>missions have been proposed. ''The reconnaissance is over," Belton said.
>''It's time to get into the detailed exploration phase."
>NEO News (now starting its second decade of distribution) is an informal
>compilation of news and opinion dealing with Near Earth Objects (NEOs) and
>their impacts. These opinions are the responsibility of the individual
>authors and do not represent the positions of NASA, the International
>Astronomical Union, or any other organization. To subscribe (or
>unsubscribe) contact dmorrison at arc.nasa.gov. For additional information,
>please see the website http://impact.arc.nasa.gov. If anyone wishes to copy
>or redistribute original material from these notes, fully or in part,
>please include this disclaimer.
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